Add metrics for style update time before FCP.

third_party/WebKit/Source/core/css/CSSTiming.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/css/CSSTiming.h"
 
 #include "core/paint/PaintTiming.h"
 
 namespace blink {
 
 static const char kSupplementName[] = "CSSTiming";
 
 CSSTiming& CSSTiming::from(Document& document) {
   CSSTiming* timing = static_cast<CSSTiming*>(
       Supplement<Document>::from(document, kSupplementName));
   if (!timing) {
     timing = new CSSTiming(document);
     Supplement<Document>::provideTo(document, kSupplementName, timing);
   }
   return *timing;
 }
 
 void CSSTiming::recordAuthorStyleSheetParseTime(double seconds) {
   if (!m_paintTiming->firstContentfulPaint())
     m_parseTimeBeforeFCP += seconds;
 }
 
+void CSSTiming::recordUpdateDuration(double seconds) {
+  if (!m_paintTiming->firstContentfulPaint())
+    m_updateTimeBeforeFCP += seconds;
+}
+
 DEFINE_TRACE(CSSTiming) {
   visitor->trace(m_document);
   visitor->trace(m_paintTiming);
   Supplement<Document>::trace(visitor);
 }
 
 CSSTiming::CSSTiming(Document& document)
     : m_document(document), m_paintTiming(PaintTiming::from(document)) {}
 
 }  // namespace blink